Free Fatty Acid Impairment of Nitric Oxide Production in Endothelial Cells Is Mediated by IKKβ

Mechanisms linking obesity to hypertension

Obesity-related hypertension is increasingly recognized as a distinct hypertensive phenotype requiring a modified approach to diagnosis and management. In this review rapidly evolving insights into the complex and interdependent mechanisms linking obesity to hypertension are discussed. Overweight and obesity are associated with adipose tissue dysfunction, characterized by enlarged hypertrophied adipocytes, increased infiltration by macrophages and marked changes in secretion of adipokines and free fatty acids. This results in chronic vascular inflammation, oxidative stress, activation of the renin-angiotensin-aldosterone system and sympathetic overdrive, eventually leading to hypertension. These mechanisms may provide novel targets for anti-hypertensive drug treatment. Recognition of obesity-related hypertension as a distinct diagnosis enables tailored therapy in clinical practice. This includes lifestyle modification and accommodated choice of blood pressure-lowering drugs.

Insulin resistance, metabolic stress, and atherosclerosis

Atherosclerosis, a pathological process that underlies the development of cardiovascular disease, is the primary cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). T2DM is characterized by hyperglycemia and insulin resistance (IR), in which target tissues fail to respond to insulin. Systemic IR is associated with impaired insulin signaling in the metabolic tissues and vasculature. Insulin receptor is highly expressed in the liver, muscle, pancreas, and adipose tissue. It is also expressed in vascular cells. It has been suggested that insulin signaling in vascular cells regulates cell proliferation and vascular function. In this review, we discuss the association between IR, metabolic stress, and atherosclerosis with focus on 1) tissue and cell distribution of insulin receptor and its differential signaling transduction and 2) potential mechanism of insulin signaling impairment and its role in the development of atherosclerosis and vascular function in metabolic disorders including hyperglycemia, hypertension, dyslipidemia, and hyperhomocysteinemia. We propose that insulin signaling impairment is the foremost biochemical mechanism underlying increased cardiovascular morbidity and mortality in atherosclerosis, T2DM, and metabolic syndrome.

Triacylglycerols and body fat mass are possible independent predictors of C3 in apparently healthy young Brazilian adults

OBJECTIVE

To evaluate the association between serum concentrations of complement factor-3 (C3) with anthropometric, biochemical, and lifestyle features in healthy young adults.

METHODS

From 157 young healthy adults 18 to 35 y old, anthropometric measurements and body composition, systolic and diastolic blood pressures, and lifestyle data were collected and analyzed. Blood samples were collected after a 12-h fast for the determination of glucose, triacylglycerols, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, insulin, C3, ceruloplasmin, and uric acid.

RESULTS

Complement factor-3 correlated directly with body mass index (r = 0.23417, P = 0.0032), body fat mass (bioelectrical impedance analysis; r = 0.33407, P < 0.0001), percentage of body fat (bioelectrical impedance analysis; r = 0.26873, P = 0.0007), waist circumference (r = 0.21266, P = 0.0075), insulin (r = 0.26152, P = 0.0009), homeostasis model assessment of insulin resistance (r = 0.24831, P = 0.0017), total cholesterol (r = 0.23335, P = 0.0033), triacylglycerols (r = 0.38435, P < 0.0001), and other outcome measurements. In the multiple linear regression analysis, triacylglycerols (r(2) = 0.1379, P < 0.0001) and body fat mass (bioelectrical impedance analysis; r(2) = 0.0621, P = 0.0010) were independently associated with the C3 concentration after adjusting for age, gender, smoking status, and physical activity.

CONCLUSION

Complement factor-3 seems to be related to several anthropometric and biochemical measurements in healthy young adults. These results demonstrate an independent role of triacylglycerols, a component of the metabolic syndrome, and body fat mass as possible predictors of C3 concentrations. Thus, C3 can be used as an early marker for metabolic syndrome manifestations.

Trans fatty acids induce vascular inflammation and reduce vascular nitric oxide production in endothelial cells

Intake of trans fatty acids (TFA), which are consumed by eating foods made from partially hydrogenated vegetable oils, is associated with a higher risk of cardiovascular disease. This relation can be explained by many factors including TFA's negative effect on endothelial function and reduced nitric oxide (NO) bioavailability. In this study we investigated the effects of three different TFA (2 common isomers of C18 found in partially hydrogenated vegetable oil and a C18 isomer found from ruminant-derived—dairy products and meat) on endothelial NF-κB activation and nitric oxide (NO) production. Human endothelial cells were treated with increasing concentrations of Elaidic (trans-C18:1 (9 trans)), Linoelaidic (trans-C18:2 (9 trans, 12 trans)), and Transvaccenic (trans-C18:1 (11 trans)) for 3 h. Both Elaidic and Linoelaidic acids were associated with increasing NF-κB activation as measured by IL-6 levels and phosphorylation of IκBα, and impairment of endothelial insulin signaling and NO production, whereas Transvaccenic acid was not associated with these responses. We also measured superoxide production, which has been hypothesized to be necessary in fatty acid-dependent activation of NF-κB. Both Elaidic acid and Linoelaidic acid are associated with increased superoxide production, whereas Transvaccenic acid (which did not induce inflammatory responses) did not increase superoxide production. We observed differential activation of endothelial superoxide production, NF-κB activation, and reduction in NO production by different C18 isomers suggesting that the location and number of trans double bonds effect endothelial NF-κB activation.

The link between metabolic abnormalities and endothelial dysfunction in type 2 diabetes: an update

Despite abundant clinical evidence linking metabolic abnormalities to diabetic vasculopathy, the molecular basis of individual susceptibility to diabetic vascular complications is still largely undetermined. Endothelial dysfunction in diabetes-associated vascular complications is considered an early stage of vasculopathy and has attracted considerable research interests. Type 2 diabetes is characterized by metabolic abnormalities, such as hyperglycemia, excess liberation of free fatty acids (FFA), insulin resistance and hyperinsulinemia. These abnormalities exert pathological impact on endothelial function by attenuating endothelium-mediated vasomotor function, enhancing endothelial apoptosis, stimulating endothelium activation/endothelium-monocyte adhesion, promoting an atherogenic response and suppressing barrier function. There are multiple signaling pathways contributing to the adverse effects of glucotoxicity on endothelial function. Insulin maintains the normal balance for release of several factors with vasoactive properties. Abnormal insulin signaling in the endothelium does not affect the whole-body glucose metabolism, but impairs endothelial response to insulin and accelerates atherosclerosis. Excessive level of FFA is implicated in the pathogenesis of insulin resistance. FFA induces endothelial oxidative stress, apoptosis and inflammatory response, and inhibits insulin signaling. Although hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia independently contribute to endothelial dysfunction via various distinct mechanisms, the mutual interactions may synergistically accelerate their adverse effects. Oxidative stress and inflammation are predicted to be among the first alterations which may trigger other downstream mediators in diabetes associated with endothelial dysfunction. These mechanisms may provide insights into potential therapeutic targets that can delay or reverse diabetic vasculopathy.

High-sucrose diet increases ROS generation, FFA accumulation, UCP2 level, and proton leak in liver mitochondria

Obesity, a risk factor for insulin resistance, contributes to the development of type 2 diabetes and cardiovascular diseases. The relationship between increased levels of free fatty acids in the liver mitochondria, mitochondrial function, and ROS generation in rat model of obesity induced by a high-sucrose diet was not sufficiently established. We determined how the bioenergetic functions and ROS generation of the mitochondria respond to a hyperlipidemic environment. Mitochondria from sucrose-fed rats generated H(2)O(2) at a higher rate than the control mitochondria. Adding fatty acid-free bovine serum albumin to mitochondria from sucrose-fed rats significantly reduced the rate of H(2)O(2) generation. In contrast, adding exogenous oleic or linoleic acid exacerbated the rate of H(2)O(2) generation in both sucrose-fed and control mitochondria, and the mitochondria from sucrose-fed rats were more sensitive than the control mitochondria. The increased rate of H(2)O(2) generation in sucrose-fed mitochondria corresponded to decreased levels of reduced GSH and vitamin E and increased levels of Cu/Zn-SOD in the intermembrane space. There was no difference between the levels of lipid peroxidation and protein carbonylation in the two types of mitochondria. In addition to the normal activity of Mn-SOD, GPX and catalase detected an increased activity of complex II, and upregulation of UCP2 was observed in mitochondria from sucrose-fed rats, all of which may accelerate respiration rates and reduce generation of ROS. In turn, these effects may protect the mitochondria of sucrose-fed rats from oxidative stress and preserve their function and integrity. However, in whole liver these adaptive mechanisms of the mitochondria were inefficient at counteracting redox imbalances and inhibiting oxidative stress outside of the mitochondria.

Chronic exposure to high fatty acids impedes receptor agonist-induced nitric oxide production and increments of cytosolic Ca2+ levels in endothelial cells

Dyslipidemia is a common metabolic disorder in diabetes. Nitric oxide (NO) production from endothelium plays the primary role in endothelium-mediated vascular relaxation and other endothelial functions. Therefore, we investigated the effects of elevated free fatty acids (FFA) on the stimulation of NO production by phospholipase C (PLC)-activating receptor agonists (potent physiological endothelium-dependent vasodilators) and defined the possible alterations of signaling pathways implicated in this scenario. Exposure of bovine aortic endothelial cells (BAECs) to high concentrations of a mixture of fatty acids (oleate and palmitate) for 5 or 10 days significantly reduced NO production evoked by receptor agonists (bradykinin or ATP) in a time- and dose-dependent manner. Such defects were not associated with alterations of either endothelial NO synthase mass or inositol phospholipid contents but were probably due to reduced elevations of intracellular free Ca(2)(+) levels ([Ca(2)(+)](i)) under these conditions. Exposure of BAECs to FFA significantly attenuated agonist-induced [Ca(2)(+)](i) increases by up to 54% in a dose- and time-dependent manner. Moreover, bradykinin receptor affinity on the cell surface was significantly decreased by high concentrations of FFA. The morphology of BAECs was altered after 10-day culture with high FFA. Co-culture with protein kinase C (PKC) inhibitors or antioxidants was able to reverse the impairments of receptor agonist-induced NO production and [Ca(2)(+)](i) rises as well as the alteration of receptor affinity in BAECs exposed to FFA. These data indicate that chronic exposure to high FFA reduces NO generation in endothelial cells probably by impairing PLC-mediated Ca(2)(+) signaling pathway through activation of PKC and excess generation of oxidants.

Endothelial NO/cGMP/VASP signaling attenuates Kupffer cell activation and hepatic insulin resistance induced by high-fat feeding

OBJECTIVE

Proinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.

RESEARCH DESIGN AND METHODS

Effect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos(-/-) mice, and Vasp(-/-) mice fed a low-fat or high-fat diet.

RESULTS

We show that high-fat feeding induces proinflammatory activation of Kupffer cells in wild-type mice coincident with reduced liver endothelial nitric oxide synthase activity and NO content while, conversely, enhancement of signaling downstream of endogenous NO by phosphodiesterase-5 inhibition protects against high fat-induced inflammation in Kupffer cells. Furthermore, proinflammatory activation of Kupffer cells is evident in eNos(-/-) mice even on a low-fat diet. Targeted deletion of vasodilator-stimulated phosphoprotein (VASP), a key downstream target of endothelially derived NO, similarly predisposes to hepatic and Kupffer cell inflammation and abrogates the protective effect of NO signaling in both macrophages and hepatocytes studied in a cell culture model.

CONCLUSIONS

These results collectively imply a physiological role for endothelial NO to limit obesity-associated inflammation and insulin resistance in hepatocytes and support a model in which Kupffer cell activation during high-fat feeding is dependent on reduced NO signaling. Our findings also identify the NO/VASP pathway as a novel potential target for the treatment of obesity-associated liver insulin resistance.

DHA-rich fish oil reverses the detrimental effects of saturated fatty acids on postprandial vascular reactivity

BACKGROUND

Experimental elevation of nonesterified fatty acids (NEFAs) impairs endothelial function, but the effect of NEFA composition is unknown.

OBJECTIVE

The objective was to test the effect of acute elevation of NEFAs enriched with either saturated fatty acids (SFAs) or SFAs with long-chain (LC) n-3 (omega-3) PUFAs on vascular function measured via flow-mediated dilatation (FMD), laser Doppler iontophoresis (LDI), and digital volume pulse (DVP).

DESIGN

In 59 subjects (30 men and 29 women), repeated oral fat feeding of either palm stearin (SFA) or palm stearin with DHA-rich fish oil (SFA + LC n-3 PUFA) was performed on 2 separate occasions with continuous heparin infusion to elevate NEFAs for a duration of 60 to 240 min. Vascular function was measured at baseline and at the end of NEFA elevation; venous blood was collected for measurement of lipids and circulating markers of endothelial function.

RESULTS

NEFA elevation during consumption of the SFA-rich drinks was associated with a marked impairment of FMD, whereas consumption of SFAs + LC n-3 PUFAs improved FMD response, with a mean (±SEM) difference of 2.06 ± 0.29% (P < 0.001). Positive correlations were found with percentage weight of LC n-3 PUFAs in circulating NEFAs and change in FMD response [Spearman's rho (r(s)) = 0.460, P < 0.001]. LDI measures increased during both treatments (P ≤ 0.026), and there was no change in DVP indexes.

CONCLUSIONS

The composition of NEFAs can acutely affect FMD. The beneficial effect of LC n-3 PUFAs on postprandial vascular function warrants further investigation but may be mediated by nitric oxide-independent mechanisms. This trial is registered at clinicaltrials.gov as NCT01351324.

Vaspin protects vascular endothelial cells against free fatty acid-induced apoptosis through a phosphatidylinositol 3-kinase/Akt pathway

Vaspin, an adipocytokine recently identified in a rat model of type 2 diabetes, has been suggested to have an insulin-sensitizing effect. However, the exact mechanism underlying this action has not been fully elucidated. Furthermore, the specific function of vaspin is largely unknown, especially in vascular cells. We examined whether vaspin affects the insulin-signaling pathway in cultured endothelial cells and is capable of preventing free fatty acid (FFA)-induced apoptosis in endothelial cells through its insulin sensitizing effect, specifically, through its stimulatory effect on PI3-kinase/Akt signaling pathways. Vaspin significantly increased Akt phosphorylation and prevented the impairment of Akt phosphorylation by linoleic acid (LA) in insulin-stimulated endothelial cells, which effects were abolished by pretreatment with the PI3-kinase inhibitor, Wortmannin. Moreover, pretreatment with vaspin prevented LA-induced apoptosis in insulin-stimulated endothelial cells; this anti-apoptotic effect of vaspin was also eliminated by pretreatment with Wortmannin. The present study indicates that vaspin protects vascular endothelial cells from FFA-induced apoptosis through upregulation of the PI3-kinase/Akt signaling pathway. Our study is the first to demonstrate that vascular cells can be targets of vaspin. Our results further suggest that vaspin could have beneficial effects on the atherosclerosis.

Effect of age on interdependence and hierarchy of cardiovascular risk factors in hypertensive patients

The prognostic significance, interdependence, and hierarchy of cardiovascular risk factors could evolve with advancing age. Our study reports on the interdependence among blood pressure (BP), other metabolic syndrome components, and high-sensitivity C-reactive protein according to age in hypertensive subjects. A total of 5,712 nondiabetic patients (50.1% men, age range 40 to 95 years) evaluated in outpatient hypertension clinics were included and divided into 5 age groups (age 40 to 49, 50 to 59, 60 to 69, 70 to 79, and >80 years). BP, evaluated by both office and 24-hour ambulatory BP monitoring, and the metabolic and inflammation parameters were determined after a ≥2-week drug washout period. The prevalence of the metabolic syndrome (Adult Treatment Panel III definition) remained stable across the age groups. We observed a stable or increased association between waist circumference and insulin resistance (Homeostasis Model of Assessment-Insulin Resistance index) and fasting plasma glucose. However, the association between waist circumference and ambulatory BP monitoring systolic BP (r(2) decrease from 9.9% to 1.0%, p <0.001), high-density lipoprotein cholesterol (r(2) decreased from 21% to 4.9%, p = 0.002), and triglyceride levels (r(2) decreased from 17.5% to 1.9%, p <0.001) decreased with age. High-sensitivity C-reactive protein correlated with all metabolic syndrome components in all age groups (p <0.001 for all). It became the strongest determinant of ambulatory BP monitoring systolic BP (p <0.001) and high-density lipoprotein cholesterol (p <0.05) in patients >80 years old. In contrast, its association with waist circumference markedly decreased. In conclusion, hypertension and dyslipidemia, but not fasting plasma glucose, dissociate from central obesity with advancing age. They are increasingly determined by low-grade inflammation, independently of central obesity. These changing associations might underlie the weakening of obesity as a cardiovascular risk factor in older persons.

Regulation of Inducible Nitric Oxide Synthase (iNOS) and its Potential Role in Insulin Resistance, Diabetes and Heart Failure

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. NO is a reactive oxygen species as well as a reactive nitrogen species. It is a free radical which mediates several biological effects. It is clear that the generation and actions of NO under physiological and pathophysiological conditions are regulated and extend to almost every cell type and function within the circulation. In mammals 3 distinct isoforms of NOS have been identified: neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS). The important isoform in the regulation of insulin resistance (IR) is iNOS. Understanding the molecular mechanisms regulating the iNOS pathway in normal and hyperglycemic conditions would help to explain some of vascular abnormalities observed in type 2 diabetes mellitus (T2DM). Previous studies have reported increased myocardial iNOS activity and expression in heart failure (HF). This review considers the recent animal studies which focus on the understanding of regulation of iNOS activity/expression and the role of iNOS agonists as potential therapeutic agents in treatment of IR, T2DM and HF.

Salsalate attenuates free fatty acid-induced microvascular and metabolic insulin resistance in humans

OBJECTIVE

Insulin recruits muscle microvasculature, thereby increasing endothelial exchange surface area. Free fatty acids (FFAs) cause insulin resistance by activating inhibitor of κB kinase β. Elevating plasma FFAs impairs insulin's microvascular and metabolic actions in vivo. Whether salsalate, an anti-inflammatory agent, prevents FFA-induced microvascular and/or metabolic insulin resistance in humans is unknown.

RESEARCH DESIGN AND METHODS

Eleven healthy, young adults were studied three times in random order. After an overnight fast, on two occasions each subject received a 5-h systemic infusion of Intralipid ± salsalate pretreatment (50 mg/kg/day for 4 days). On the third occasion, saline replaced Intralipid. A 1 mU/kg/min euglycemic insulin clamp was superimposed over the last 2-h of each study. Skeletal and cardiac muscle microvascular blood volume (MBV), microvascular flow velocity (MFV), and microvascular blood flow (MBF) were determined before and after insulin infusion. Whole body glucose disposal rates were calculated from glucose infusion rates.

RESULTS

Insulin significantly increased skeletal and cardiac muscle MBV and MBF without affecting MFV. Lipid infusion abolished insulin-mediated microvascular recruitment in both skeletal and cardiac muscle and lowered insulin-stimulated whole body glucose disposal (P<0.001). Salsalate treatment rescued insulin's actions to recruit muscle microvasculature and improved insulin-stimulated whole body glucose disposal in the presence of high plasma FFAs.

CONCLUSIONS

High plasma concentrations of FFAs cause both microvascular and metabolic insulin resistance, which can be prevented or attenuated by salsalate treatment. Our data suggest that treatments aimed at inhibition of inflammatory response might help alleviate vascular insulin resistance and improve metabolic control in patients with diabetes.

The impact of the metabolic syndrome--but not of hypertension--on all-cause mortality disappears in the elderly

OBJECTIVE

The metabolic syndrome predicts the risk of cardiovascular and all-cause death, but its clinical relevance in the elderly remains debatable. We aimed to determine the impact of the metabolic syndrome on all-cause mortality according to age, in comparison with hypertension alone.

METHODS

We studied 129 655 participants (82 110 men and 47 545 women) undergoing a standard health check-up at the Investigations Préventives et Cliniques center (Paris, France). Mean follow-up was 4.9±2.6 years. The prevalence of the metabolic syndrome and its components was determined according to age group (<55, 55-65, >65 years old). All-cause mortality according to metabolic syndrome and age was determined using Cox regression model analysis, unadjusted or adjusted for age, sex, smoking and other confounding factors.

RESULTS

The prevalence of the metabolic syndrome and all its components except lipid parameters strongly increased with age. All-cause mortality associated with the metabolic syndrome (using three different definitions) was significantly elevated in participants below 55 years old, and was little affected by adjustment for confounding factors. However, it decreased from 1.77 (1.45-2.16) in participants below 55 years old to 1.12 (0.84-1.48) in participants above 65 years old [hazard ratio (95% confidence interval); National Cholesterol Education Program definition]. Waist circumference, fasting blood glucose and lipid parameters failed to predict mortality in participants above 65 years old. In contrast, hypertension (blood pressure>140/90 mmHg or treatment) remained a significant predictor of all-cause mortality [hazard ratio 1.30 (95% confidence interval 1.02-1.66)] in participants above 65 years old.

CONCLUSIONS

In a setting representative of primary care, hypertension but not the metabolic syndrome remains a strong risk factor for all-cause mortality in participants above 65 years old.

Macrovascular angiopathy in children and adolescents with type 1 diabetes

Diabetes represents one of the most common diseases globally. Worryingly, the worldwide incidence of type 1 diabetes (T1D) is rising by 3% per year. Despite the rapid increase in diabetes incidence, recent advances in diabetes treatment have been successful in decreasing morbidity and mortality from diabetes-related retinopathy, nephropathy, and neuropathy. In contrast, there is clear evidence for the lack of improvement in mortality for cardiovascular diseases (CVDs). This emphasizes the importance of focusing childhood diabetes care strategies for the prevention of CVD in adulthood. Furthermore, although most work on diabetes and macrovascular disease relates to type 2 diabetes, it has been shown that the age-adjusted relative risk of CVD in T1D far exceeds that in type 2 diabetes. As T1D appears predominantly during childhood, those with T1D are at greater risk for coronary events early in life and require lifelong medical attention. Because of the important health effects of CVDs in children and adolescents with T1D, patients, family members, and care providers should understand the interaction of T1D and cardiovascular risk. In addition, optimal cardiac care for the patient with diabetes should focus on aggressive management of traditional cardiovascular risk factors to optimize those well-recognized as well as new specific risk factors which are becoming available. Therefore, a complete characterization of the molecular mechanisms involved in the development and progression of macrovascular angiopathy is needed. Furthermore, as vascular abnormalities begin as early as in childhood, potentially modifiable risk factors should be identified at an early stage of vascular disease development.

Hypertension management and microvascular insulin resistance in diabetes

Type 2 diabetes is in essence a vascular disease and is frequently associated with hypertension, macrovascular events, and microvascular complications. Microvascular dysfunction, including impaired recruitment and capillary rarefaction, has been implicated in the pathogenesis of diabetic complications. Microvascular insulin resistance and renin-angiotensin system upregulation are present in diabetes, and each contributes to the development of hypertension and microvascular dysfunction. In the insulin-sensitive state, insulin increases microvascular perfusion by increasing endothelial nitric oxide production, but this effect is abolished by insulin resistance. Angiotensin II, acting via the type 1 receptors, induces inflammation and oxidative stress, leading to impaired insulin signaling, reduced nitric oxide availability, and vasoconstriction. Conversely, it acts on the type 2 receptors to cause vasodilatation. Because substrate and hormonal exchanges occur in the microvasculature, antihypertensive agents targeted to improve microvascular insulin sensitivity and function may have beneficial effects beyond their capacity to lower blood pressure in patients with diabetes.

Palmitate induces C-reactive protein expression in human aortic endothelial cells. Relevance to fatty acid-induced endothelial dysfunction

Circulating levels of free fatty acids are commonly elevated in patients with the metabolic syndrome and exert, through activating proinflammatory pathways, harmful effects of the vascular endothelium. In this study, we examined the effect of palmitate (PA) on endothelial C-reactive protein (CRP) expression and the role of CRP in PA-induced nitric oxide (NO) inhibition. Palmitate increased, in a dose-dependent manner, CRP protein expression and production in human aortic endothelial cells (HAECs). Induction of CRP protein was mimicked by ceramide, whereas bromopalmitate and other common free fatty acids such as oleate or linoleate were ineffective. Palmitate also elicited reactive oxygen species production in HAECs, an effect prevented by protein kinase C (PKC) inhibition and adenosine monophosphate-activated kinase (AMPK) activation. Palmitate-treated HAECs showed increased CRP messenger RNA expression and nuclear factor (NF)-κB activation. Induction of CRP expression by PA was prevented by antioxidants and normalized by PKC and mitogen-activated protein kinase inhibitors. Disrupting NF-κB and Janus kinase/signal transducers and activators of transcription pathways or inducing AMPK activation also suppressed the stimulatory effect of PA on CRP messenger RNA expression. Finally, in HAECs, PA reduced NO release, an effect reversed by anti-CRP antibody. These data demonstrate that PA-induced endothelial CRP expression involves PKC-driven oxidative stress, possibly through AMPK inhibition, and activation of downstream redox-sensitive signaling pathways, including NF-κB. They further support a role for endothelial cell-derived CRP as mediator of the suppressive effect of PA on NO production.

Plasma esterified and non-esterified fatty acids metabolic profiling using gas chromatography-mass spectrometry and its application in the study of diabetic mellitus and diabetic nephropathy

Using gas chromatography-mass spectrometry (GC-MS), a new metabolic profiling method was established to assess the levels of non-esterified fatty acids (NEFAs) and esterified fatty acids (EFAs) in plasma. The extraction method was simple and robust without removing protein process. With this method 25 fatty acids (FAs), both EFAs and NEFAs, can be recognized simultaneously with only 10 μL plasma. 15 of the 25 can be precisely quantified. The method was validated and then applied into clinical metabonomics research. Five clinical groups including 150 cases were involved. The relationship between FA levels and diabetic mellitus (DM) as well as diabetic nephropathy (DN) pathology was speculated. Furthermore, the possible pathological causes and effects were discussed in detail. Potential biomarkers (p value <0.01) were screened with Student's t-test. With the application of partial least squares-discriminant analysis (PLS-DA), different stages were distinguished. The result may be useful for the pathology study of metabolic syndromes, and may also be helpful for monitoring the progression of DM and DN.

Loss of insulin-mediated microvascular perfusion in skeletal muscle is associated with the development of insulin resistance

AIM

The aetiology of the development of type 2 diabetes remains unresolved. In the present study, we assessed whether an impairment of insulin-mediated microvascular perfusion occurs early in the onset of insulin resistance.

MATERIALS AND METHODS

Hooded Wistar rats were fed either a normal diet (ND) or a high-fat diet (HFD) for 4 weeks. Anaesthetized animals were subjected to an isoglycaemic hyperinsulinaemic clamp (3 or 10 mU/min/kg x 2 h), and measurements were made of glucose infusion rate (GIR), hindleg glucose uptake, muscle glucose uptake by 2-deoxy-d-glucose (R'g), glucose appearance (Ra), glucose disappearance (Rd), femoral blood flow (FBF) and hindleg 1-methylxanthine disappearance (1-MXD, an index of microvascular perfusion).

RESULTS

Compared with ND-fed animal, HFD feeding led to a mild increase in fasting plasma glucose and plasma insulin, without an increase in total body weight. During the clamps, HFD rats showed an impairment of insulin-mediated action on GIR, hindleg glucose uptake, R'g, Ra, Rd and FBF, with a greater loss of insulin responsiveness at 3 mU/min/kg than at 10 mU/min/kg. The HFD also impaired insulin-mediated microvascular perfusion as assessed by 1-MXD. Interestingly, 1-MXD was the only measurement that remained unresponsive to the higher dose of 10 mU/min/kg insulin.

CONCLUSIONS

We conclude that the early stage of insulin resistance is characterized by an impairment of the insulin-mediated microvascular responses in skeletal muscle. This is likely to cause greater whole body insulin resistance by limiting the delivery of hormones and nutrients to muscle.

Free fatty acids induce endothelial dysfunction and activate protein kinase C and nuclear factor-κB pathway in rat aorta

BACKGROUND

Insulin resistance is associated with an inappropriate elevation of plasma free fatty acids (FFAs) and endothelial dysfunction. In this study, we asked if elevated circulating FFA levels led to impaired insulin signaling and endothelial dysfunction in-vivo via activation of PKC-mediated inflammatory pathways.

METHODS

Sprague-Dawley (S-D) rats were infused with 1) 20% intralipid+heparin (FFA group) or 2) saline alone (Control group) for 6h. The intact aorta thoracica and aorta abdominalis were then removed. Aortic rings were isolated and evaluated for endothelial-dependent and non-dependent relaxation in an organ bath. The activities of eNOS and PKC were measured in endothelial homogenates prepared from endothelial cells harvested from the aorta. The expression levels of insulin signaling molecules IRS-1, Akt, eNOS, ERK1/ERK2, PKC-α, NFκB-p65 subunit and IκB-α in rat aortic endothelium were determined by immunohistochemistry and Western blot.

RESULTS

Elevation of FFAs resulted in a 35.9% reduction in the response to acetylcholine (p < 0.01), a 26% decline in plasma NOx levels (p < 0.05), a 53% decrease in eNOS activity and a 34 ± 9% inhibition in IRS-1 tyrosine phosphorylation (p < 0.05). We also found a 46% decrease in Akt phosphorylation and a 36% decrease in eNOS phosphorylation. FFA-induced endothelial insulin resistance was associated with 82% increase in total membrane-associated PKC activity, a 1.7-fold increase in total PKC-α protein, 1.29-fold decrease in IκB-α expression levels and 1.47-fold increase in NF-κB p65 subunit expression in rat aortic endothelium.

CONCLUSION

The molecular mechanisms underlying FFA-induced endothelial insulin resistance and eNOS inhibition may provide an important link implicating the PKC and IκB-α/NF-κB pathways in FFA-mediated inhibition of vascular insulin signaling.

The tsim tsoum approaches for prevention of cardiovascular disease

The Tsim Tsoum Concept means that humans evolved on a diet in which nature recommends to ingest fatty acids in a balanced ratio (polyunsaturated(P) : saturated(S) =w-6 : w-3 = 1 : 1)as part of dietary lipid pattern where monounsaturated fatty acids(MUFA) is the major fatty acid(P : M : S = 1 : 6 : 1) in the background of other dietary factors; antioxidants, vitamins, minerals and fiber as well as physical activity and low mental stress. Several hundred years ago, our diet included natural foods; fruits, vegetables, green vegetables, seeds, eggs and honey. Fish, and wild meat were also available to pre-agricultural humans which shaped modern human genetic nutritional requirement. Cereal grains (refined), and vegetable oils that are rich in w-6 fatty acids are relatively recent addition to the human diet that represent dramatic departure from those foods to which we are adapted. Excess of linoleic acid, trans fatty acids (TFA), saturated and total fat as well as refined starches and sugar are proinflammatory. Low dietary MUFA and n-3 fatty acids and other long chain polyunsarurated fatty acids (LCPUFA) are important in the pathogenesis of metabolic syndrome. Increased sympathetic activity with greater secretion of neurotransmitters in conjunction of underlying long chain PUFA deficiency, and excess of proinflammatory nutrients, may damage the neurons via proinflammatory cytokines, in the ventromedial hypothalamus and insulin receptors in the brain.Since, 30–50% of the fatty acids in the brain are LCPUFA, especially omega-3 fatty acids, which are incorporated in the cell membrane phospholipids, it is possible that their supplementation may be protective.Blood lipid composition does reflect one's health status: (a) circulating serum lipoproteins and their ratio provide information on their atherogenicity to blood vessels and (b) circulating plasma fatty acids, such as w-6/w-3 fatty acid ratio, give indication on proinflammatory status of blood vessels, cardiomyocytes, liver cells and neurones; (a) and (b) are phenotype-related and depend on genetic, environmental and developmental factors. As such, they appear as universal markers for holistic health and these may be important in the pathogenesis of cardiovascular diseases and cancer, which is the main consideration of Tsim Tsoum concept.

Cultured hypothalamic neurons are resistant to inflammation and insulin resistance induced by saturated fatty acids

Hypothalamic inflammation induced by high-fat feeding causes insulin and leptin resistance and contributes to the pathogenesis of obesity. Since in vitro exposure to saturated fatty acids causes inflammation and insulin resistance in many cultured cell types, we determined how cultured hypothalamic neurons respond to this stimulus. Two murine hypothalamic neuronal cell cultures, N43/5 and GT1-7, were exposed to escalating concentrations of saturated fatty acids for up to 24 h. Harvested cells were evaluated for activation of inflammation by gene expression and protein content. Insulin-treated cells were evaluated for induction of markers of insulin receptor signaling (p-IRS, p-Akt). In both hypothalamic cell lines, inflammation was induced by prototypical inflammatory mediators LPS and TNFalpha, as judged by induction of IkappaBalpha (3- to 5-fold) and IL-6 (3- to 7-fold) mRNA and p-IkappaBalpha protein, and TNFalpha pretreatment reduced insulin-mediated p-Akt activation by 30% (P < 0.05). By comparison, neither mixed saturated fatty acid (100, 250, or 500 microM for <or=6 h) nor palmitate exposure alone (200 microM for <or=24 h) caused inflammatory activation or insulin resistance in cultured hypothalamic neurons, whereas they did in control muscle and endothelial cell lines. Despite the lack of evidence of inflammatory signaling, saturated fatty acid exposure in cultured hypothalamic neurons causes endoplasmic reticulum stress, induces mitogen-activated protein kinase, and causes apoptotic cell death with prolonged exposure. We conclude that saturated fatty acid exposure does not induce inflammatory signaling or insulin resistance in cultured hypothalamic neurons. Therefore, hypothalamic neuronal inflammation in the setting of DIO may involve an indirect mechanism mediated by saturated fatty acids on nonneuronal cells.

Endothelial dysfunction in diabetes mellitus: molecular mechanisms and clinical implications

Cardiovascular disease is a major complication of diabetes mellitus, and improved strategies for prevention and treatment are needed. Endothelial dysfunction contributes to the pathogenesis and clinical expression of atherosclerosis in diabetes mellitus. This article reviews the evidence linking endothelial dysfunction to human diabetes mellitus and experimental studies that investigated the responsible mechanisms. We then discuss the implications of these studies for current management and for new approaches for the prevention and treatment of cardiovascular disease in patients with diabetes mellitus.

Elevated plasma free fatty acids increase cardiovascular risk by inducing plasma biomarkers of endothelial activation, myeloperoxidase and PAI-1 in healthy subjects

Background

CVD in obesity and T2DM are associated with endothelial activation, elevated plasma vascular inflammation markers and a prothrombotic state. We examined the contribution of FFA to these abnormalities following a 48-hour physiological increase in plasma FFA to levels of obesity and diabetes in a group of healthy subjects.

Methods

40 non-diabetic subjects (age = 38 ± 3 yr, BMI = 28 ± 1 kg/m², FPG = 95 ± 1 mg/dl, HbA_1c = 5.3 ± 0.1%) were admitted twice and received a 48-hour infusion of normal saline or low-dose lipid. Plasma was drawn for intracellular (ICAM-1) and vascular (VCAM-1) adhesion molecules-1, E-selectin (sE-S), myeloperoxidase (MPO) and total plasminogen inhibitor-1 (tPAI-1). Insulin sensitivity was measured by a hyperglycemic clamp (M/I).

Results

Lipid infusion increased plasma FFA to levels observed in obesity and T2DM and reduced insulin sensitivity by 27% (p = 0.01). Elevated plasma FFA increased plasma markers of endothelial activation ICAM-1 (138 ± 10 vs. 186 ± 25 ng/ml), VCAM-1 (1066 ± 67 vs. 1204 ± 65 ng/ml) and sE-S (20 ± 1 vs. 24 ± 1 ng/ml) between 13-35% and by ≥ 2-fold plasma levels of myeloperoxidase (7.5 ± 0.9 to 15 ± 25 ng/ml), an inflammatory marker of future CVD, and tPAI-1 (9.7 ± 0.6 to 22.5 ± 1.5 ng/ml), an indicator of a prothrombotic state (all p ≤ 0.01). The FFA-induced increase was independent from the degree of adiposity, being of similar magnitude in lean, overweight and obese subjects.

Conclusions

An increase in plasma FFA within the physiological range observed in obesity and T2DM induces markers of endothelial activation, vascular inflammation and thrombosis in healthy subjects. This suggests that even transient (48-hour) and modest increases in plasma FFA may initiate early vascular abnormalities that promote atherosclerosis and CVD.

Reduced NO-cGMP signaling contributes to vascular inflammation and insulin resistance induced by high-fat feeding

OBJECTIVE

Diet-induced obesity (DIO) in mice causes vascular inflammation and insulin resistance that are accompanied by decreased endothelial-derived NO production. We sought to determine whether reduced NO-cGMP signaling contributes to the deleterious effects of DIO on the vasculature and, if so, whether these effects can be blocked by increased vascular NO-cGMP signaling.

METHODS AND RESULTS

By using an established endothelial cell culture model of insulin resistance, exposure to palmitate, 100 micromol/L, for 3 hours induced both cellular inflammation (activation of IKK beta-nuclear factor-kappaB) and impaired insulin signaling via the insulin receptor substrate-phosphatidylinositol 3-kinase pathway. Sensitivity to palmitate-induced endothelial inflammation and insulin resistance was increased when NO signaling was reduced using an endothelial NO synthase inhibitor, whereas endothelial responses to palmitate were blocked by pretreatment with either an NO donor or a cGMP analogue. To investigate whether endogenous NO-cGMP signaling protects against vascular responses to nutrient excess in vivo, adult male mice lacking endothelial NO synthase were studied. As predicted, both vascular inflammation (phosphorylated I kappaB alpha and intercellular adhesion molecule levels) and insulin resistance (phosphorylated Akt [pAkt] and phosphorylated eNOS [peNOS] levels) were increased in endothelial NO synthase(-/-) (eNOS(-/-)) mice, reminiscent of the effect of DIO in wild-type controls. Next, we asked whether the vascular response to DIO in wild-type mice can be reversed by a pharmacological increase of cGMP signaling. C57BL6 mice were either fed a high-fat diet or remained on a low-fat diet for 8 weeks. During the final 2 weeks of the study, mice on each diet received either placebo or the phosphodiesterase-5 inhibitor sildenafil, 10 mg/kg per day orally. In high-fat diet-fed mice, vascular inflammation and insulin resistance were completely prevented by sildenafil administration at a dose that had no effect in mice fed the low-fat diet.

CONCLUSIONS

Reduced signaling via the NO-cGMP pathway is a mediator of vascular inflammation and insulin resistance during overnutrition induced by high-fat feeding. Therefore, phosphodiesterase-5, soluble guanylyl cyclase, and other molecules in the NO-cGMP pathway (eg, protein kinase G) constitute potential targets for the treatment of vascular dysfunction in the setting of obesity.

Role of insulin resistance and lipotoxicity in non-alcoholic steatohepatitis

It is well established that the development of NAFLD and NASH are closely linked to an excess flow of free fatty acids (FFA) arising from dysfunctional/insulin resistant adipose tissue causing ectopic fat deposition in many organs. In the liver, when chronic lipid supply surpasses the metabolic ability to adapt it will induce hepatocellular damage as FFA are redirected into harmful pathways of non-oxidative metabolism with intracellular accumulation of toxic lipid-derived metabolites. Multiple mechanisms have been implicated including mitochondrial dysfunction, endoplasmic reticulum stress, and activation of multiple inflammatory pathways. Understanding the role of insulin resistance and lipotoxicity in NASH as part of a broader metabolic disorder is likely to assist practitioners in the successful management of these challenging patients.

Insulin resistance, lipotoxicity and endothelial dysfunction

The number of people with the insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity has reached epidemic proportions worldwide. Eighty percent of people with T2DM will die from the complications of cardiovascular atherosclerosis. Insulin resistance is characterised by endothelial dysfunction, which is a pivotal step in the initiation/progression of atherosclerosis. A hallmark of endothelial dysfunction is an unfavourable imbalance between the bioavailability of the antiatherosclerotic signalling molecule nitric oxide (NO) and proatherosclerotic reactive oxygen species. In this review we discuss the mechanisms linking insulin resistance to endothelial dysfunction, with a particular emphasis on a potential role for a toxic effect of free fatty acids on endothelial cell homeostasis.

The trafficking/interaction of eNOS and caveolin-1 induced by insulin modulates endothelial nitric oxide production

Endothelial nitric oxide synthase (eNOS) activity is tightly regulated by posttranscriptional modification and its subcellular localization. Here we examined whether insulin modulates nitric oxide (NO) production by regulating eNOS subcellular localization. We used confocal microscopy and immunoblots to examine the time course for 1) subcellular targeting/association of eNOS and caveolin-1 (CAV-1); 2) eNOS Ser(1179) phosphorylation; and 3) NO production in cultured bovine aorta endothelial cells. Serum starvation increased eNOS/CAV-1 localization to the perinuclear region. Adding insulin provoked their prompt translocation to and association at the plasma membrane (PM). Specific monoclonal antibodies against either CAV-1 or eNOS coimmunoprecipitated the other from bovine aorta endothelial cell membrane extracts, and insulin increased this interaction. Insulin stimulated NO production transiently despite a persistent eNOS Ser(1179) phosphorylation. The decline of NO production correlated temporally to insulin-induced translocation of eNOS and CAV-1 to PM. Knockdown of CAV-1 expression with a specific small interfering RNA duplex resulted in eNOS redistributing to the perinuclear region and nearly doubled insulin-induced NO production. Inhibition of phosphatidylinositol 3-kinase activity with wortmannin not only significantly inhibited insulin-induced translocation of eNOS and CAV-1 to PM but also blocked insulin-induced interaction of CAV-1 with eNOS at PM. Insulin increased incorporation of [(3)H]palmitic acid into eNOS immunoprecipitates by approximately 140%. Insulin-induced translocation of eNOS and CAV-1 to PM was palmitoylation dependent. Inhibiting eNOS and CAV-1 palmitoylation enhanced the NO production while blocking the translocation of eNOS and CAV-1 to PM induced by insulin. These data show that insulin acutely regulates eNOS and CAV-1 trafficking to PM of vascular endothelial cells where their interaction can regulate eNOS activity.

Infusing lipid raises plasma free fatty acids and induces insulin resistance in muscle microvasculature

CONTEXT

Insulin recruits muscle microvasculature, which increases the endothelial exchange surface area to facilitate substrate delivery. Elevated plasma concentrations of free fatty acids (FFAs) cause insulin resistance.

OBJECTIVES

The aim of the study was to examine whether FFAs cause insulin resistance in human muscle microvasculature.

SETTING

The study was conducted at the General Clinical Research Center at the University of Virginia.

METHODS

Twenty-two healthy subjects were studied under two protocols designed to raise plasma insulin concentrations to postprandial levels using either an insulin infusion or a mixed meal challenge. Within each protocol, subjects were studied twice. In random order, they received a 5-h systemic infusion of either saline or Intralipid/heparin. Three hours into the infusion, baseline muscle microvascular blood volume (MBV), microvascular flow velocity, and microvascular blood flow (MBF) were measured. Each subject was then given either the mixed meal or a 1 mU/kg x min insulin clamp for 2 h. Microvascular parameters were again obtained 2 h after the meal or at the end of insulin infusion.

RESULTS

Meal feeding and insulin infusion raised plasma insulin concentrations to approximately 200 pm, and each significantly increased muscle MBV (P = 0.03 and P < 0.01, respectively). MBF trended up after meal feeding (P = 0.08) and increased significantly after insulin infusion (P = 0.02). In the presence of Intralipid, neither the meal nor the insulin infusion increased muscle MBV and MBF.

CONCLUSIONS

Compared to saline, lipid infusion raises plasma FFA concentrations and blocks the ability of insulin or meal to recruit muscle microvasculature. High plasma FFA concentrations may contribute to muscle insulin resistance and the microvascular complications of diabetes.

Effects of exercise training and diet on lipid kinetics during free fatty acid-induced insulin resistance in older obese humans with impaired glucose tolerance

Elevated free fatty acids (FFA) are implicated with insulin resistance at the cellular level. However, the contribution of whole body lipid kinetics to FFA-induced insulin resistance is not well understood, and the effect of exercise and diet on this metabolic defect is not known. We investigated the effect of 12 wk of exercise training with and without caloric restriction on FFA turnover and oxidation (FFA(ox)) during acute FFA-induced insulin resistance. Sixteen obese subjects with impaired glucose tolerance were randomized to either a hypocaloric (n = 8; -598 +/- 125 kcal/day, 66 +/- 1 yr, 32.8 +/- 1.8 kg/m(2)) or a eucaloric (n = 8; 67 +/- 2 yr, 35.3 +/- 2.1 kg/m(2)) diet and aerobic exercise (1 h/day at 65% of maximal oxygen uptake) regimen. Lipid kinetics ([1-(14)C]palmitate) were assessed throughout a 7-h, 40 mU x m(-2) x min(-1) hyperinsulinemic euglycemic clamp, during which insulin resistance was induced in the last 5 h by a sustained elevation in plasma FFA (intralipid/heparin infusion). Despite greater weight loss in the hypocaloric group (-7.7 +/- 0.5 vs. -3.3 +/- 0.7%, P < 0.001), FFA-induced peripheral insulin resistance was improved equally in both groups. However, circulating FFA concentrations (2,123 +/- 261 vs. 1,764 +/- 194 micromol/l, P < 0.05) and FFA turnover (3.20 +/- 0.58 vs. 2.19 +/- 0.58 micromol x kg FFM(-1) x min(-1), P < 0.01) during hyperlipemia were suppressed only in the hypocaloric group. In contrast, whole body FFA(ox) was improved in both groups at rest and during hyperlipemia. These changes were driven by increases in intracellular lipid-derived FFA(ox) (12.3 +/- 7.7 and 14.7 +/- 7.8%, P < 0.05). We conclude that the exercise-induced improvement in FFA-induced insulin resistance is independent of the magnitude of weight loss and FFA turnover, yet it is linked to increased intracellular FFA utilization.

Activation of NF-kappaB by palmitate in endothelial cells: a key role for NADPH oxidase-derived superoxide in response to TLR4 activation

OBJECTIVE

We investigated whether NADPH oxidase-dependent production of superoxide contributes to activation of NF-kappaB in endothelial cells by the saturated free fatty acid palmitate.

METHODS AND RESULTS

After incubation of human endothelial cells with palmitate at a concentration known to induce cellular inflammation (100 mumol/L), we measured superoxide levels by using electron spin resonance spectroscopy and the spin trap 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH). Palmitate exposure induced a >2-fold increase in superoxide levels, an effect associated with activation of NF-kappaB signaling as measured by phospho-IkappaBalpha, NF-kappaB activity, IL-6, and ICAM expression. Reduction in superoxide levels by each of 3 different interventions-pretreatment with superoxide dismutase (SOD), diphenylene iodinium (DPI), or knockdown of NADPH oxidase 4 (NOX4) by siRNA-attenuated palmitate-mediated NF-kappaB signaling. Inhibition of toll like receptor-4 (TLR4) signaling also suppressed palmitate-mediated superoxide production and associated inflammation, whereas palmitate-mediated superoxide production was not affected by overexpression of a phosphorylation mutant IkappaBalpha (NF-kappaB super repressor) that blocks cellular inflammation downstream of IKKbeta/NF-kappaB. Finally, high-fat feeding increased expression of NOX4 and an upstream activator, bone morphogenic protein (BMP4), in thoracic aortic tissue from C57BL/6 mice, but not in TLR4(-/-) mice, compared to low-fat fed controls.

CONCLUSIONS

These results suggest that NADPH oxidase-dependent superoxide production links palmitate-stimulated TLR4 activation to NF-kappaB signaling in endothelial cells.

The vascular actions of insulin control its delivery to muscle and regulate the rate-limiting step in skeletal muscle insulin action

Evidence suggests that insulin delivery to skeletal muscle interstitium is the rate-limiting step in insulin-stimulated muscle glucose uptake and that this process is impaired by insulin resistance. In this review we examine the basis for the hypothesis that insulin acts on the vasculature at three discrete steps to enhance its own delivery to muscle: (1) relaxation of resistance vessels to increase total blood flow; (2) relaxation of pre-capillary arterioles to increase the microvascular exchange surface perfused within skeletal muscle (microvascular recruitment); and (3) the trans-endothelial transport (TET) of insulin. Insulin can relax resistance vessels and increase blood flow to skeletal muscle. However, there is controversy as to whether this occurs at physiological concentrations of, and exposure times to, insulin. The microvasculature is recruited more quickly and at lower insulin concentrations than are needed to increase total blood flow, a finding consistent with a physiological role for insulin in muscle insulin delivery. Microvascular recruitment is impaired by obesity, diabetes and nitric oxide synthase inhibitors. Insulin TET is a third potential site for regulating insulin delivery. This is underscored by the consistent finding that steady-state insulin concentrations in plasma are approximately twice those in muscle interstitium. Recent in vivo and in vitro findings suggest that insulin traverses the vascular endothelium via a trans-cellular, receptor-mediated pathway, and emerging data indicate that insulin acts on the endothelium to facilitate its own TET. Thus, muscle insulin delivery, which is rate-limiting for its metabolic action, is itself regulated by insulin at multiple steps. These findings highlight the need to further understand the role of the vascular actions of insulin in metabolic regulation.

Hypothalamic proinflammatory lipid accumulation, inflammation, and insulin resistance in rats fed a high-fat diet

Weight gain induced by an energy-dense diet is hypothesized to arise in part from defects in the neuronal response to circulating adiposity negative feedback signals, such as insulin. Peripheral tissue insulin resistance involves cellular inflammatory responses thought to be invoked by excess lipid. Therefore, we sought to determine whether similar signaling pathways are activated in the brain of rats fed a high-fat (HF) diet. The ability of intracerebroventricular (icv) insulin to reduce food intake and activate hypothalamic signal transduction is attenuated in HF-fed compared with low-fat (LF)-fed rats. This effect was accompanied by both hypothalamic accumulation of palmitoyl- and stearoyl-CoA and activation of a marker of inflammatory signaling, inhibitor of kappaB kinase-beta (IKKbeta). Hypothalamic insulin resistance and inflammation were observed with icv palmitate infusion or HF feeding independent of excess caloric intake. Last, we observed that central IKKbeta inhibition reduced food intake and was associated with increased hypothalamic insulin sensitivity in rats fed a HF but not a LF diet. These data collectively support a model of diet-induced obesity whereby dietary fat, not excess calories, induces hypothalamic insulin resistance by increasing the content of saturated acyl-CoA species and activating local inflammatory signals, which result in a failure to appropriately regulate food intake.

Contribution of insulin and Akt1 signaling to endothelial nitric oxide synthase in the regulation of endothelial function and blood pressure

Impaired insulin signaling via phosphatidylinositol 3-kinase/Akt to endothelial nitric oxide synthase (eNOS) in the vasculature has been postulated to lead to arterial dysfunction and hypertension in obesity and other insulin resistant states. To investigate this, we compared insulin signaling in the vasculature, endothelial function, and systemic blood pressure in mice fed a high-fat (HF) diet to mice with genetic ablation of insulin receptors in all vascular tissues (TTr-IR(-/-)) or mice with genetic ablation of Akt1 (Akt1-/-). HF mice developed obesity, impaired glucose tolerance, and elevated free fatty acids that was associated with endothelial dysfunction and hypertension. Basal and insulin-mediated phosphorylation of extracellular signal-regulated kinase 1/2 and Akt in the vasculature was preserved, but basal and insulin-stimulated eNOS phosphorylation was abolished in vessels from HF versus lean mice. In contrast, basal vascular eNOS phosphorylation, endothelial function, and blood pressure were normal despite absent insulin-mediated eNOS phosphorylation in TTr-IR(-/-) mice and absent insulin-mediated eNOS phosphorylation via Akt1 in Akt1-/- mice. In cultured endothelial cells, 6 hours of incubation with palmitate attenuated basal and insulin-stimulated eNOS phosphorylation and NO production despite normal activation of extracellular signal-regulated kinase 1/2 and Akt. Moreover, incubation of isolated arteries with palmitate impaired endothelium-dependent but not vascular smooth muscle function. Collectively, these results indicate that lower arterial eNOS phosphorylation, hypertension, and vascular dysfunction following HF feeding do not result from defective upstream signaling via Akt, but from free fatty acid-mediated impairment of eNOS phosphorylation.

Dietary saturated and unsaturated fats as determinants of blood pressure and vascular function

The amount and type of dietary fat have long been associated with the risk of CVD. Arterial stiffness and endothelial dysfunction are important risk factors in the aetiology of CHD. A range of methods exists to assess vascular function that may be used in nutritional science, including clinic and ambulatory blood pressure monitoring, pulse wave analysis, pulse wave velocity, flow-mediated dilatation and venous occlusion plethysmography. The present review focuses on the quantity and type of dietary fat and effects on blood pressure, arterial compliance and endothelial function. Concerning fat quantity, the amount of dietary fat consumed habitually appears to have little influence on vascular function independent of fatty acid composition, although single high-fat meals postprandially impair endothelial function compared with low-fat meals. The mechanism is related to increased circulating lipoproteins and NEFA which may induce pro-inflammatory pathways and increase oxidative stress. Regarding the type of fat, cross-sectional data suggest that saturated fat adversely affects vascular function whereas polyunsaturated fat (mainly linoleic acid (18 : 2n-6) and n-3 PUFA) are beneficial. EPA (20 : 5n-3) and DHA (22 : 6n-3) can reduce blood pressure, improve arterial compliance in type 2 diabetics and dyslipidaemics, and augment endothelium-dependent vasodilation. The mechanisms for this vascular protection, and the nature of the separate physiological effects induced by EPA and DHA, are priorities for future research. Since good-quality observational or interventional data on dietary fatty acid composition and vascular function are scarce, no further recommendations can be suggested in addition to current guidelines at the present time.

Intricacies of fat

One of the most exciting cell biology fields of study concerns the physiology and pathology of fat. The basic assumptions once held concerning the function of adipose tissue have been shown to be oversimplified or sometimes completely wrong. Fat does more than store excess energy; it is actually the largest endocrine organ in the body, and it may be one of the most active. Adipocytes release hormones and other molecules that act on nearby tissues and travel through the vasculature to distant sites, such as the brain, skeletal muscle, and liver. Under conditions of normal weight, those signals help the body to suppress hunger, utilize glucose, and decrease the risk of cardiovascular disease. However, under conditions of obesity, the hormones (or the proteins that bind the hormones) become abnormal and can result in states of chronic inflammation leading to diabetes and heart disease. In addition, excessive fat can lead to the accumulation of lipid droplets in nonfat cells, including skeletal and cardiac muscle. Although some lipid droplets are used as an immediate source of energy for cells, large numbers of stored droplets can cause cellular damage and cell death. The purposes of this article are to review the normal and deviant signals released by fat cells, to draw a link between those signals and chronic diseases such as diabetes, and to discuss the role of exercise in reversing some of the deviant signaling perpetrated by excess fat.

High glucose-induced IKK-Hsp-90 interaction contributes to endothelial dysfunction

A decline in the bioavailability of nitric oxide (NO) that causes endothelial dysfunction is a hallmark of diabetes. The availability of NO to the vasculature is regulated by endothelial nitric oxide synthase (eNOS) activity and the involvement of heat shock protein-90 (Hsp-90) in the regulation of eNOS activity has been demonstrated. Hsp-90 has been shown to interact with upstream kinases [inhibitor kappaB kinases (IKK)alpha, beta, and gamma] in nonvascular cells. In this study, we have investigated the interaction of Hsp-90-IKKbeta in endothelial cells under conditions of high glucose (HG) as a possible mechanism that diminishes Hsp-90-eNOS interaction, which could contribute to reduced bioavailability of NO. We report for the first time that IKKbeta interacts with Hsp-90, and this interaction is augmented by HG in vascular endothelial cells. HG also augments transcriptional (3.5 +/- 0.65-fold) and translational (1.97 +/- 0.17-fold) expression as well as the catalytic activity of IKKbeta (2.45 +/- 0.4-fold). Both IKKbeta and eNOS could be coimmunoprecipitated with Hsp-90. Inhibition of Hsp-90 with geldanamycin (2 microM) or Radicicol (20 microM) mitigated (0.45 +/- 0.04-fold and 0.93 +/- 0.16-fold, respectively) HG induced-IKKbeta activity (2.5 +/- 0.42-fold). Blocking of IKKbeta expression by IKK inhibitor II (15 microM wedelolactone) or small interferring RNA (siRNA) improved Hsp-90-eNOS interaction and NO production under conditions of HG. These results illuminate a possible mechanism for the declining eNOS activity reported under conditions of HG.

Endothelial dysfunction and diabetes: roles of hyperglycemia, impaired insulin signaling and obesity

Endothelial dysfunction comprises a number of functional alterations in the vascular endothelium that are associated with diabetes and cardiovascular disease, including changes in vasoregulation, enhanced generation of reactive oxygen intermediates, inflammatory activation, and altered barrier function. Hyperglycemia is a characteristic feature of type 1 and type 2 diabetes and plays a pivotal role in diabetes-associated microvascular complications. Although hyperglycemia also contributes to the occurrence and progression of macrovascular disease (the major cause of death in type 2 diabetes), other factors such as dyslipidemia, hyperinsulinemia, and adipose-tissue-derived factors play a more dominant role. A mutual interaction between these factors and endothelial dysfunction occurs during the progression of the disease. We pay special attention to the possible involvement of endoplasmic reticulum stress (ER stress) and the role of obesity and adipose-derived adipokines as contributors to endothelial dysfunction in type 2 diabetes. The close interaction of adipocytes of perivascular adipose tissue with arteries and arterioles facilitates the exposure of their endothelial cells to adipokines, particularly if inflammation activates the adipose tissue and thus affects vasoregulation and capillary recruitment in skeletal muscle. Hence, an initial dysfunction of endothelial cells underlies metabolic and vascular alterations that contribute to the development of type 2 diabetes.

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle

Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.

Vascular inflammation, insulin resistance, and reduced nitric oxide production precede the onset of peripheral insulin resistance

OBJECTIVE

Obesity causes inflammation and insulin resistance in the vasculature as well as in tissues involved in glucose metabolism such as liver, muscle, and adipose tissue. To investigate the relative susceptibility of vascular tissue to these effects, we determined the time course over which inflammation and insulin resistance develops in various tissues of mice with diet-induced obesity (DIO) and compared these tissue-based responses to changes in circulating inflammatory markers.

METHODS AND RESULTS

Adult male C57BL/6 mice were fed either a control low-fat diet (LF; 10% saturated fat) or a high-fat diet (HF, 60% saturated fat) for durations ranging between 1 to 14 weeks. Cellular inflammation and insulin resistance were assessed by measuring phospho-IkappaBalpha and insulin-induced phosphorylation of Akt, respectively, in extracts of thoracic aorta, liver, skeletal muscle, and visceral fat. As expected, HF feeding induced rapid increases of body weight, fat mass, and fasting insulin levels compared to controls, each of which achieved statistical significance within 4 weeks. Whereas plasma markers of inflammation became elevated relatively late in the course of DIO (eg, serum amyloid A [SAA], by Week 14), levels of phospho-IkappaBalpha in aortic lysates were elevated by 2-fold within the first week. The early onset of vascular inflammation was accompanied by biochemical evidence of both endothelial dysfunction (reduced nitric oxide production; induction of intracellular adhesion molecule-1 and vascular cell adhesion molecule-1) and insulin resistance (impaired insulin-induced phosphorylation of Akt and eNOS). Although inflammation and insulin resistance were also detected in skeletal muscle and liver of HF-fed animals, these responses were observed much later (between 4 and 8 weeks of HF feeding), and they were not detected in visceral adipose tissue until 14 weeks.

CONCLUSIONS

During obesity induced by HF feeding, inflammation and insulin resistance develop in the vasculature well before these responses are detected in muscle, liver, or adipose tissue. This observation suggests that the vasculature is more susceptible than other tissues to the deleterious effects of nutrient overload.

An integrated view of insulin resistance and endothelial dysfunction

Endothelial dysfunction and insulin resistance are frequently comorbid states. Vasodilator actions of insulin are mediated by phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathways that stimulate production of nitric oxide from vascular endothelium. This helps to couple metabolic and hemodynamic homeostasis under healthy conditions. In pathologic states, shared causal factors, including glucotoxicity, lipotoxicity, and inflammation selectively impair PI3K-dependent insulin signaling pathways that contribute to reciprocal relationships between insulin resistance and endothelial dysfunction. This article discusses the implications of pathway-selective insulin resistance in vascular endothelium, interactions between endothelial dysfunction and insulin resistance, and therapeutic interventions that may simultaneously improve both metabolic and cardiovascular physiology in insulin-resistant conditions.

Effects of dietary supplementation with the green tea polyphenol epigallocatechin-3-gallate on insulin resistance and associated metabolic risk factors: randomized controlled trial

Animal evidence indicates that green tea may modulate insulin sensitivity, with epigallocatechin-3-gallate (EGCG) proposed as a likely health-promoting component. The purpose of this study was to investigate the effect of dietary supplementation with EGCG on insulin resistance and associated metabolic risk factors in man. Overweight or obese male subjects, aged 40-65 years, were randomly assigned to take 400 mg capsules of EGCG (n 46) or the placebo lactose (n 42), twice daily for 8 weeks. Oral glucose tolerance testing and measurement of metabolic risk factors (BMI, waist circumference, percentage body fat, blood pressure, total cholesterol, LDL-cholesterol, HDL-cholesterol, TAG) was conducted pre- and post-intervention. Mood was evaluated weekly using the University of Wales Institute of Science and Technology mood adjective checklist. EGCG treatment had no effect on insulin sensitivity, insulin secretion or glucose tolerance but did reduce diastolic blood pressure (mean change: placebo - 0.058 (se 0.75) mmHg; EGCG - 2.68 (se 0.72) mmHg; P = 0.014). No significant change in the other metabolic risk factors was observed. The EGCG group also reported feeling in a more positive mood than the placebo group across the intervention period (mean score for hedonic tone: EGCG, 29.11 (se 0.44); placebo, 27.84 (se 0.46); P = 0.048). In conclusion, regular intake of EGCG had no effect on insulin resistance but did result in a modest reduction in diastolic blood pressure. This antihypertensive effect may contribute to some of the cardiovascular benefits associated with habitual green tea consumption. EGCG treatment also had a positive effect on mood. Further studies are needed to confirm the findings and investigate their mechanistic basis.

Protective effects of a compound herbal extract (Tong Xin Luo) on free fatty acid induced endothelial injury: implications of antioxidant system

Background

Tong-Xin-Luo (TXL) – a mixture of herbal extracts, has been used in Chinese medicine with established therapeutic efficacy in patients with coronary artery disease.

Methods

We investigated the protective role of TXL extracts on endothelial cells injured by a known risk factor – palmitic acid (PA), which is elevated in metabolic syndrome and associated with cardiovascular complications. Human aortic endothelial cells (HAECs) were preconditioned with TXL extracts before exposed to PA for 24 hours.

Results

We found that PA (0.5 mM) exposure induced 73% apoptosis in endothelial cells. However, when HAECs were preconditioned with ethanol extracted TXL (100 μg/ml), PA induced only 7% of the endothelial cells into apoptosis. Using antibody-based protein microarray, we found that TXL attenuated PA-induced activation of p38-MAPK stress pathway. To investigate the mechanisms involved in TXL's protective effects, we found that TXL reduced PA-induced intracellular oxidative stress. Through AMPK pathway, TXL restored the intracellular antioxidant system, which was depressed by the PA treatment, with an increased expression of thioredoxin and a decreased expression of the thioredoxin interacting protein.

Conclusion

In summary, our study demonstrates that TXL protects endothelial cells from PA-induced injury. This protection is likely mediated by boosting intracellular antioxidant capacity through AMPK pathway, which may account for the therapeutic efficacy in TXL-mediated cardiovascular protection.